1. Field of the Invention
The present invention relates to an inspection method, etc. for degradation of a lithium ion secondary battery.
2. Description of the Related Art
Automobiles or railway vehicles have secondary batteries mounted thereon such as a lead acid battery, a nickel metal hydride battery, and a lithium ion battery, charge an electric power obtained by a regeneration brake to the secondary batteries, and utilize the electric power obtained upon acceleration, etc. Such secondary batteries are used for hybrid cars in which improved fuel consumption is achieved, and electric cars driven by electric energy stored in the secondary batteries. Further, it is requested in the field of wind power generation or solar power generation that leveling in a load by using a secondary battery system be attained upon connections with a power transmission system so that renewable energy subject to fluctuations may be converted into electricity.
It is very important to know the state of degradation of secondary batteries being used in the secondary battery systems for use in vehicles such as hybrid cars and electric cars or power storage. Further, also when a secondary battery that has been degraded to some extent is diverted to other uses, it is necessary to exactly know how much the secondary battery in question has been degraded.
For example, a method of detecting the state of degradation of a secondary battery is described in JP-2003-308885-A. JP-2003-308885-A involves measuring, at about 1 C rate and at lower than 0.1 C rate, a voltage change profile just before charging or discharging is completed, and comparing the same with each other before and after degradation, thereby determining the degree of degradation of a positive electrode and a negative electrode constituting the battery.
To improve the accuracy in detection of the degradation of a secondary battery, JP-2010-54428-A discloses that means is provided for measuring the temperature of a secondary battery to be subjected to a charge-discharge test and temperature is measured in addition to voltage and current values based on charge-discharge current, thereby improving the accuracy in detection of degradation.
In JP-2010-261807-A, direct current resistance is estimated based on each of the fluctuating components of current and voltage to examine the state of degradation of a battery in use, thereby judging the state of degradation.
Further, JP-2010-40318-A discloses a method in which a plurality of acoustic emission sensors are attached to a battery to investigate the internal state of the battery, thereby detecting where in the inside of the battery the acoustic emission is generated. JP-2009-170348-A and JP-2009-176511-A disclose examples of use of acoustic emission as a method of examining the characteristics of the secondary battery.